Analysis of cytochrome P-450 function was analyzed with the two complementary methods of inhibitory monoclonal antibodies and cDNA expression. The MAb techniques were used to analyze stereospecific metabolism of benzo(a)pyrene, nitropyrene toluene, methyl-N-amyl- nitrosamine. Other studies concerned 8-methoxy psoralen metabolism and DNA binding. The MAbs also were used to analyze the mechanism of P-450 inhibitors of heme destruction. The cDNA expressed P-450s were characterized for their enzyme activity and mutagen activation for hydrocarbons, heterocyclic amine food pyrolysate products, aflatoxin and nitroasamines. The cDNA expression systems utilized a lytic vaccinia virus vector yielding a large number of animal and human P-450s that could be expressed in various host cells including human cells. The cDNAs were also expressed within a stable transfection in a human lymphoblastoid cell line. The complementary methods define the role and contribution of individual P-450s in drug and carcinogen detoxification and activation.